Arrangement of tube circuits in supercritical forced through-flow vapor generator



Nov. 29, 1966 W. W. SCHROEDTER ARRANGEMENT OF TUBE CIRCUITS IN SUPERCRITICAL FORCED THROUGH-FLOW VAPOR GENERATOR Filed Dec. l, 1965 2 Sheets-Sheet l www HVU

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BY ma AGENT N0V 29, 1966 w. w. scHRoEDTER 3,288,117

ARRANGEMENT OF TUBE CIRCUITS IN SUPERCRITICAL FORCED THROUGH*FLOW VAPOR GENERATOR Filed Dec. l, 1965 2 Sheets-Sheet a 4Z ExTEN- REAR HANGER REAR 30 ROOF SION PASS HANGER TUBES PASS SIDE SIDE TUBES REAR REAR wALI. wALI.. F wALI.

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WILLBURT W. SCHROEDTER INVENTOR.

AGENT United States Patent Utilice 3,Z88,ll7 Patented Nov. 29, 1966 3,238,117 ARRANGEMENT F TUBE CHKCUITS IN SUPER- CRITICAL FORCED THROUGH-FLOW VAPOR GENERATR Willburt W. Schroedter, West Hartford, Conn., assigner to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed Dec. 1, 1965, Ser. No. 510,924 8 Claims. (Cl. 122-406) The invention relates in general to forced through flow vapor generators and is more specifically directed to an arrangement of the tube circuits of a vapor generator in which steam of high temperature is produced at supercritical pressure, and in which these tube circuits form tubular heat absorbing surfaces which line the Walls of the furnace chamber and of the gas passages associated therewith.

In modern steam generators of the forced through ow type operating at or above the so-called critical pressure point, i.e., operating in the supercritical pressure region, separation of steam and water does not occur and a constant temperature is not maintained while evaporatiton takes place, as is the case when operating in the subcritical pressure region. To the contrary, in steam generators operating at supercritical pressure, the temperature of the working fluid entering the heating surfaces increases steadily while the fluid absorbs heat in passing through these heating surfaces until a maximum desired temperature at the superheater outlet is reached.

` In the type of forced through flow generator to which the present invention is particularly applicable the working fluid ows from an inlet point to an outlet point through a number of parallel through flow heat absorbing circuits. In order to avoid the starving of any of these circuits and to prevent heat damage to the tubes, it is important that a desired predetermined flow be maintained in each circuit while the pressure drop through all the parallel circuits is the same. This has heretofore been accomplished by adding a resistance in the form of orifices to those circuits which would have a lower pressure drop for a desired flow. Adding orifices to the ilow circuits for balancing purpose, however, is uneconomical inasmuch as it undesirably increases the power requirements of the feed pump.

The present invention reduces the over-all pressure drop through the circuits by means of an arrangement in which the heating surface location, heat absorption rate and uid velocity in each circuit is novelly coordinated with those of the remaining circuits so as to achieve a balance which makes the addition of resistances in the most active circuit superfluous. Substantial savings in feed pump power and a more uniform heat absorption with elimination of hot spots are thereby obtained.

In addition, in supercritical steam boilers where each through ow circuit comprises a great number of parallelly arranged tubes lining the furnace walls each parallel stream of fluid passing through a tube may absorb a different amount of heat and, therefore, acquire a different temperature and volume than those of other parallel iiuid streams. It is therefore extremely important that the fluid flowing through the individual parallel tubes be mixed at given intermediate locations in the ow circuit to assure a nearly uniform ow and temperature in al1 tubes. This has heretofore been accomplished by providing mixing headers at locations intermediate the height of the furnace wall. However, placing headers in these intermediate locations in the furnace walls seriously complicates the construction of a gas-tight wall structure and prevents a smooth, even wall surface devoid of refractory surface to which slag may cling. The invention overcomes this difficulty by placing mixing headers between entire walls such as, for example, between the front wall and the roof, or between the rear wall of the furnace and the rear wall of the rear gas pass.

Furthermore, in steam boilers having a gas pass extending laterally from the upper region of the furnace, vertical hanger tubes must be provided which pass through the lateral gas pass in the plane of the rear wall for suspending the rear wall tubes therefrom. Formerly, all the rear wall tubes after forming the rear wall nose arch were brought up vertically through the laterally extending gas pass. A large number of these were brought up in the plane of the rear wall to serve as hanger tubes for the rear wall and the remaining tubes in the plane of the front wall of the rear gas pass. This design left wide open gaps in the oor of the lateral or horizontal gas pass which gaps had to be closed with widely spaced tubes having wide fins. Because of insufficient cooling due to the wide spacing the fin tubes were subject to costly high temperature heat damage.

In accordance with the invention, arranging the flow circuits in the novel manner herein proposed, this damage is now avoided by utilizing all the rear wall tubes in forming the bottom or iioor of the laterally extending gas pass. Accordingly these tubes now retain the close spacing of the rear wall tubes, with hanger supports for the rear wall being provided separately and in an entirely new manner as will be described in more detail hereinbelow.

In addition, the inventive design permits the use of a fusion welded type wall throughout the rear wall nose arch and the horizontal or lateral gas pass bottom. This type of wall is disclosed in U.S. Patent 2,719,210, issued to E. C. Chapman on September 27, 1955; and in U.S. Patent 2,987,052, issued to W. H. Armacost on June 6, 1961. The use of this fusion welded tube wall makes possible the employment of modern shop practices such as gang bending and gang welding as disclosed in U.S. Patent 2,946,116, issued to W. C. Norris et al. on July 26, 1960; and in U.S. Patent 3,168,129, issued to S. P. Henry on February 2, 1965. Such modern shop practices can now be employed in accordance with the invention in the fabrication of the entire tube structure comprising the rear wall, nose arch and gas -pass bottom, in the shop rather than in the field. Costly field welding is thereby largely eliminated or greatly reduced.

As indicated above, in the herein disclosed arrangement of tube circuits, support of the rear wall is effected through separate hanger tubes which are independent of the rear wall tubes. These hanger tubes penetrate the fusion welded wall of the horizontal gas pass floor only at wide spacings and contrary to present practice can be selected in the proper number and size for the required load. In accordance with the invention, and as will later herein become evident, these hanger tubes egress from a mixing header and are independent of the fluid flow in the rear wall tubes in contrast to earlier designs. The flow through these hanger tubes therefore is generally uniform regardless -of possible non-uniformity of flow in the rear wall tubes. Thus such freedom in selecting hanger tube size and number eliminates the formerly required large number of riser tubes passing through the horizontal gas pass, which riser tubes were of necessity of the size of the rear wall tubes and in excess of the number of hanger tubes required to carry the load. Due to the reduced number of riser tubes the gas temperature entering the superheater tube bank is now considerably higher than before, thereby affording a substantial saving in the costly high temperature superheater tubing which generally follows the hanger tubes in the gas iiow sense.

It is accordingly a primary object of the invention to provide an arrangement of tube circuits in a supercritical forced through flow vapor generator which arrangement provides a well balanced flow through each circuit with respect to the flow through the other circuits.

It is fa lfurther object of the invention to reduce the pressure drop through the circuits and thereby reduce feed pump power requirement-s.

It is another object of the invention to provide a hanger tube support for the furnace rear wall of a supercritical forced through ow boiler, which hanger tubes are independent of the size and number of rear wall tubes.

It is a still further object of the invention to provide a tube circuit arrangement for a superc-ritical forced through flow boiler in which mixing of the fluid passing through individual tubes takes place at intermediate locations in the flow circuit, and whereby the uniform furnace wall surface presented by continuous parallel water wall tubes is maintaine-d throughout the height of the furnace walls.

Other objects an-d advantages of the invention will become apparent from the Ifollowing description of an illustrative embodiment thereof when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic elevational section through p a supercritical forced through ow steam generator showing the novel arrangement of tube circuits herein disclosed;

FIG. 2 represents a diagrammatic plan view throu-gh the upper portion of the furnace chamber, the horizontal gas pass and the rear gas pass, when taken at line 2-2 of FIG. l; f

FIG. 3 is a line diagram depicting in simplified form the herein disclosed novel flow arrangement of the tube circuits lining the walls of the furnace and the associated gas passes;

FIG. 4 is a typical cross section through a fusion welded tubular wall section, as employed in the construction of the walls of the furnace and associated gas passages; and

FIG. 5 is .a detail showing how the Hoor tubes of the horizontal gas pass are offset to provide room for passage ofthe hanger tubes.

Referring now to the drawings wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the inven- 'tion depicted therein includes a steam generator designated generally as and comprising a ffurnace chamber 11 having a front wall 12 lined with tubes 13, a rear wall 14 lined with tubes 16, `anti two opposing side walls 17 lined with tubes 18. Air and fuel for burning are introduced into the furnace by Way of burners 20, with the combustion gases leavin-g the furnace 11 by way of a horizontal gas pass 22 extending laterally from the upper region of furnace 11. The side walls 23 of the lateral gas pass 22 effectively form extensions of the furnace side walls 17 and are lined with tubes 24. Adjoining the horizontal gas pass 22 a downward or rear gas pass 26 is provided having side walls 27 which effectively form extensions of the horizontal gas pass side walls 23 and are lined with tubes 28. The rear wall 29 of the rear pass 26 is lined with tubes 30. Various heat absorbing surfaces such as, for example, superheater sections 32 and reheater sections 33 and economizer S9 are arranged in the path of combustion gases leading from the burners to the gas outlet 34.

The upper portion `of rear wall 14 is provided with a nose or arch 31 and is extended to form the floor or bottom 36 of lateral or horizontal -gas pass 22. The tubes 35 lining the nose arch 31 and the tubes 37 lining the bottom 36 are extensions of rear wall tube 16, retaining the size as well as the spacing orf these tubes, and terminate in header 39. p

Furnace 11, lateral gas pass 22 and downward gas pass 26 have a common roof which is formed by tubes 42. These tubes are effective extensions of tubes 13 lining the furnace front wall 12, and terminate in header 44.

To support the rear wall tubes 16 from an overhead steel structure indicated at 45, a first group of hanger tubes 46 is provided from which rear wall tubes 16 are suspended by means of steel rods 47 which are attached to header 48. Hanger tubes 46 pass through spaces provided between the floor tubes 37 vby offsetting these tubes as shown in FIG. 5.

The upper portion 50 of the tubes lining the front wall of the rear pass 26 likewise traverse the horizontal gas pass 22. From this second group of han-ger tubes 5) portions of the rear gas pass structure are suspended from overhead supports indicated at S2. While the lower portion 53 of these tubes comprise-s tubes that are closely spaced, the upper portion 50 comprises widely spaced tubes so as to allow for ready passage of the combustion gases. To achieve the wide spacing the tubes may be bifurcate-d, 4or offset in well-known manner similar to that illustrated in FIG. 5.

In the highly competitive eld of high pressure, forced through flow steam boilers it is very important that the heat absorbing wall surface of the furna-ce chamber and of the gas passes associated therewith be designed to afford the most economical heating surface with lrespect to fabrication cost, maintenance cost and operating eiciency. The socalled fusion welded wall as illustratively shown in FIG. 4 lfullls these requirements vto a high degree. One of the preferred methods of fabricating a fusion welde-d wall in sections of panels and of utilizing these welded tube panels in building furnace walls is described in greater detail in the afore-mentioned U.S. Patents 2,719,210; 2,987,052;f2,946,116 and 3,168,129.

The present invention in addition to other advantages makes use of the fusion welded wall surface not only in the furnace chamber walls but also in the bottom 36 of the lateral gas pass 22. Heretofore this surface could not be made of continuous fusion welded wall panels because some of the rear wall tubes had to be utilized as hanger tubes in place of hanger tubes 46, and others in place of hanger tubes 50.

The present invention separates hanger tubes 46 and 5t) entirely from the rear wall tubes in the manner earlier herein set forth. This permits a free choice of the size and of the spacing of the hanger tubes to accommodate the load requirements and at the same time to permit fusion welded wall construction for the bottom surface 36 of horizontal pass 22. Substantial savings in fabrication costs and in high temperature tubular material, as well as a gain in the heat absorbing efciency of the bottom tubes 37 are thereby achieved. Furthermore, the temperature of the gases passing through the tubular screens formed by hanger tubes 46 and 50 in accordance with the invention has been increased to such a degree that the high temperature heating surface of superheater sections 32 and 33 can be decreased by a significant amount.

To achieve the well balanced arrangement of the through ow circuits which is one ofthe main objects of the invention, the through flow is subdivided into parallel branches or circuits, with each circuit comprising a selected portion of the tubular wall surface of the furnace and of the associated gas passages. These parallel branches have their beginning at the inlet header 54 leading to the furnace waterwalls 13, 16 and 18. They terminate at the outlet header 44 where the working Huid from all circuits is collected and from whence the through flow working fluid is conducted to superheater sections 32 by means not shown. y

The feedwater entering economizer inlet hea-der 58 passes through economizer tubes 59 to the economizer outlet header 60 from whence it llows to mixing vessel 62. This vessel also receives heated recirculating working Huid from the above-mentioned outlet header 44. The recirculated huid mixes with the through flow quantity received from the economizer 59, with the mixture passing to water wall inlet header 54 by way of conduit 63 and pump 64.

Referring now to FIG. 3 the fiow of the working fluid is divided into four parallel streams. One stream enters the front wall tubes 13, a second stream the rear wall tube 16, and the third and fourth streams enter the two groups of side wall tubes 18. Each of the furnace wall circuit-s comprises a plurality of parallel vertical tubes with the flow passing therethrough in a direction from bottom to top. Mixing headers to secure uniform fiow and temperature in the various tubes are provided in each circuit at locations which do not interfere with the smooth, uniform and uninterrupted surface generally presented by the closely spaced tubes of fusion welded water Wall panels.

Considering now the individual circuits in detail, the front wall circuit originating in header 54, as in the case with the remaining circuit, comprises the front wall tubes 13, a pair of mixing headers 65 and 66 provided at the top end of the front wall, the roof tubes 42 which continuously extend throughout the roof of the furnace chamber 11, -horizontal gas pass 22 and downward gas pass 26, and finally terminate in outlet header 44.

The two side wall circuits are identical, each including side wall tubes 18, lside wall upper header 68, side wall links 69 leading to the lower side wall header 70 of the horizontal gas pass 22, extension side wall tubes 24, upper side wall header 72, and a connection to the outlet header 44. Another link 73 leads from upper furnace side wall header 68 to the lower side wall header 74 of the rear pass 26, with the working fluid passing through the side wall tubes 28 of the gas pass, the upper side wall header 75 and through connecting means to outlet header 44. Each of the side wall circuits includes a pair of mixing headers, i.e., 68, 70 and 68, 74.

The rear wall circuit comprises furnace rear wall tube 16, tubes 35 of nose arch 31, the tubes 37 of the bottom 36 of the lateral gas pass 22, and header 39. The remaining rear wall circuit is thereafter divided into three portions. One portion fiows from header 39 to header 48 lfeeding the first set of hanger tubes 46 which terminate in upper header 76, which, in t-urn, is connected with outlet header 44. The second portion of the rear wall circuit flows from header 39 to header 78 feeding the front wall tubes 53 of the rear gas pass 26 and the second hanger tubes Sil which are extensions of tubes 53. These tubes terminate in upper header 70 which, in turn, is connected with outlet header 44. The third portion of the rear wall circuit also flows from header 39 to header 78, and thence by way of link 80 to header 82 from which tube 30 lining the rear wall 29 of rear pass 26 originate. Tubes 30 also terminate in outlet header 44. In accordance with the invention the different branches of the rear wall circuit also include pairs of mixing headers as do the front and side wall circuits. Thus, after leaving the bottom tubes 37 of the lateral gas pass 22 the working fluid issuing from the different t-ubes is entirely mixed in headers 39 and 48 before flowing through hanger tubes 46. The fiuid is also thoroughly mixed in headers 39 and 78 before fiowing through tubes 53 and 50, and in headers 78 and 82 before flowing through tubes 30.

While I have illustrated and described a preferred embodiment of my invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein Without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

I claim:

1. A forced through iiow supercritical vapor generator having a through fiow circuit; an upright furnace With opposed front, rear and side walls; a gas pass extending laterally from the upper region of the furnace, said gas pass having side walls, roof and floor effectively lforming extensions of the furnace side Wall, furnace roof and furnace rear wall, respectively; a gas pass extending downwardly from the lateral gas pass, and having a front wall and a rear wall, and side walls effectively forming extensions with the lateral gas pass sidewalls; vertically extending tubes lining the vertical walls of the furnace, of the lateral gas pass and of the downward gas pass; laterally extending tubes lining the roof of the furnace, the roof of the lateral gas pass the roof of the downward gas pass and the bottom of the lateral gas pass; vertically extending first hanger tubes passing through said lateral gas pass in the plane of said rear wall tubes for suspending the rear wall tubes therefrom; vertically extending second hanger tubes passing through said lateral gas pass in the plane of the #front wall of said downward lgas pass for suspending the tubes fof the front wall of the downward gas pass therefrom; means directing a first part of said through flow in series up through said front wall tubes and through the roof tubes of said furnace, of said lateral gas pass and of said downward gas pass; means directing a second part of said through flow in series up through the side walls of said furnace, of `said lateral gas pass and of said downward gas pass; means directing a third part of said through fiow in series up through said furnace rear wall tubes, through the tubes of the bottom of said lateral gas pass, and thence in three parallel streams (a) through said first hanger tubes, (b) through the tubes of the front wall of said downward pass and said second hanger tubes, and (c) through the tubes of the rear wall of said down- Ward pass.

2. An organization as defined in claim 1 wherein two mixing headers are provided in the fiow circuit between said lfurnace front wall tubes and said furnace roof tubes to obtain uniform fluid temperature in said roof tubes.

3. An organization as defined in claim 1, wherein two mixing headers are provided in the flow circuit between the tubes of the bottom of said lateral gas pass and said first hanger tubes to 'obtain uniform fiuid temperature in said first hangertubes.

4. An organization as defined in claim 1, wherein two mixing headers are provided in the fiow circuit between the tubes of the bottom `off said lateral gas pass and said second hanger tubes, to obtain uniform fiuid temperature in said second hanger tubes.

5. An organization as defined in claim 2, wherein two mixing headers are provided in the fiow circuit between the tubes of the bottom of `said lateral gas pass and said first hanger tubes to obtain uniform fluid temperature in said roof tubes and in said first hanger tubes.

6. An organization as defined in claim 2, wherein two mixing headers are provided in the flow circuit between the tubes of the bottom of said lateral gas pass and said second hanger tubes, to obtain uniform temperature in said roof tubes.

7. An `organization as defined in claim 1, wherein two mixing headers are provided in the fiow circuit between the tubes of the bottom of said lateral gas pass and said first as well as said second hanger tubes, to obtain uniform fiuid temperature in said first and said second hanger tubes.

8. An organization as defined in claim 7 wherein two mixing headers are provided in the flow circuit between said furnace front wall tubes and said furnace roof tubes to obtain uniform fluid temperature in said roof tubes as well as in said first and said second hanger tubes.

References Cited bythe Examiner UNITED STATES PATENTS 3,125,995 3/1964 Koch.. -122-406 KENNETH W. SPRAGUE, Primary Examiner. 

1. A FORCED THROUGH FLOW SUPERCRITICAL VAPOR GENERATOR HAVING A THROUGH FLOW CIRCUIT; AN UPRIGHT FURNACE WITH OPPOSED FRONT, REAR AND SIDE WALLS; A GAS PASS EXTENDING LATERALLY FROM THE UPPER REGION OF THE FURNACE, SAID GAS PASS HAVING SIDE WALLS, ROOF AND FLOOR EFFECTIVELY FORMING EXTENSIONS OF THE FURNACE SIDE WALL, FURNACE ROOF AND FURNACE REAR WALL, RESPECTIVELY; A GAS PASS EXTENDING DOWNWARDLY FROM THE LATERAL GAS PASS, AND HAVING A FRONT WALL AND A REAR WALL, AND SIDE WALLS EFFECTIVELY FORMING EXTENSIONS WITH THE LATERAL GAS PASS SIDEWALLS; VERTICALLY EXTENDING TUBES LINING THE VERTICAL WALLS OF THE FURNACE, OF THE LATERAL GAS PASS AND OF THE DOWNWARD GAS PASS; LATERALLY EXTENDING TUBES LINING THE ROOF OF THE FURNACE, THE ROOF OF THE LATERAL GAS PASS THE ROOF OF THE DOWNWARD GAS PASS AND THE BOTTOM OF THE LATERAL GAS PASS; VERTICALLY EXTENDING FIRST HANGER TUBES PASSING THROUGH SAID LATERAL GAS PASS IN THE PLANE OF SAID REAR WALL TUBES FOR SUSPENDING THE REAR WALL TUBES THEREFROM; VERTICALLY EXTENDING SECOND HANGER TUBES PASSING THROUGH SAID LATERAL GAS PASS IN THE PLANE OF THE FRONT WALL OF SAID DOWNWARD GAS PASS FOR SUSPENDING THE TUBES OF THE FRONT WALL OF THE DOWNWARD GAS PASS THEREFROM; MEANS DIRECTING A FIRST PART OF SAID THROUGH FLOW IN SERIES UP THROUGH SAID FRONT WALL TUBES AND THROUGH THE ROOF TUBES OF SAID FURNACE, OF SAID LATERAL GAS PASS AND OF SAID DOWNWARD GAS PASS; MEANS DIRECTING A SECOND PART OF SAID THROUGH FLOW IN SERIES UP THROUGH THE SIDE WALLS OF SAID FURNACE, OF SAID LATERAL GAS PASS AND OF SAID DOWNWARD GAS PASS; MEANS DIRECTING A THIRD PART OF SAID THROUGH FLOW IN SERIES UP THROUGH SAID FURNACE REAR WALL TUBES, THROUGH THE TUBES OF THE BOTTOM OF SAID LATERAL GAS PASS, AND THENCE IN THREE PARALLEL STREAMS (A) THROUGH SAID FIRST HANGER TUBES, (B) THROUGH THE TUBES OF THE FRONT WALL OF SAID DOWNWARD PASS AND SAID SECOND HANGER TUBES, AND (C) THROUGH THE TUBES OF THE REAR WALL OF SAID DOWNWARD PASS. 